Many types of power supplies are known for powering gas discharge lamps. It is often desirable to regulate the output of the lamp to change its brightness level, or to cause it to flicker, flash or the like. In addition, the lamps characteristics change over time as the lamp ages, potentially causing the lamp to have reduced brightness. In these and other instances, it is desirable to regulate the lamp current to keep the brightness at a uniform level.
A power supply for a gas discharge lamp is disclosed that uses a unique method of regulating the lamp current. In a preferred embodiment, the power supply includes an input circuit that receives power from a power source, an output transformer having a primary winding and a secondary winding, with the lamp being connected in circuit across the secondary winding, first and second power switches that switch power to the primary winding, and a driver that drives the switches at a drive frequency. The power supply also includes a tuned LC resonant circuit having a resonant frequency, that is connected in circuit between the driver and the lamp, and a controller that generates control signals to the driver at a first frequency that is functionally related to the drive frequency. The first frequency may equal the drive frequency. The controller regulates the lamp current by controlling the difference between the resonant frequency of the LC resonant circuit and the first frequency.
The power supply operates at maximum efficiency or maximum brightness when the drive frequency is approximately equal to the resonant frequency. However, the brightness of the lamp can be reduced, dimmed and regulated by adjusting the difference between resonant frequency and the drive frequency. If the first frequency or the drive frequency is less than the resonant frequency, a decrease in the first frequency or the drive frequency will detune the tuned LC resonant circuit and the lamp current will be reduced. Likewise, if the initial drive frequency is greater than the resonant frequency, the drive frequency can be increased to also reduce the efficiency of the lamp and thus dim the lamp.
In a preferred embodiment, the transformer is a step-up transformer and the primary winding is a part of the LC resonant circuit.
The power supply preferably includes a microprocessor controller having a flash memory and an electrically erasable programmable read-only memory (EEPROM). The EEPROM may be used to store a variety of data, including run time information, fault information, and information regarding the number of ON and OFF cycles of the lamp.
Preferably, any number of operations may be performed while the software is running one or more background routines. For example, any of the following may be performed during the running of the background routine: checking for fault conditions, changing the first or drive frequencies, determining the brightness level of the lamp, resetting a watch dog timer, recording data in non-volatile memory or executing a lamp shutdown.
It is a feature and advantage of the invention to provide a power supply that operates at maximum efficiency or maximum brightness when the drive frequency is approximately equal to the resonant frequency.
It is another feature and advantage of the invention to regulate the brightness of a lamp by adjusting the difference between the resonant frequency and the drive frequency.
It is another feature and advantage of the invention to use run time information for both fault analysis and for changing operating characteristics of the power supply.
It is another feature and advantage of the invention to provide a heat detection system in the power supply to render the power supply inoperable upon the detection of over-temperature conditions.
It is another feature and advantage of the invention to provide a low-power operation mode for the power supply to minimize power consumption.
It is another feature and advantage of the invention to eliminate the need to periodically restrike the load.
It is another feature and advantage of the invention to use an electrically erasable programmable read only memory device (EEPROM) in conjunction with the power supply, and to store serial numbers and date codes in the EEPROM.
These are the features of the present invention will be apparent to those skilled in the art from the following detailed description and the drawings, in which: